Heat a nonstick skillet over medium heat, and cook chicken thighs until barely pink in the center, about 20 minutes, turning once; stir in onion and garlic, and cook and stir until onions are translucent, about 5 minutes.

Stir zucchini, carrots, and bell pepper into chicken mixture; cook and stir until vegetables are tender with a bite at the center and chicken is no longer pink at the center, about 5 minutes. An instant read thermometer inserted into the center of chicken thighs should read at least 165 degrees F (74 degrees C).

Stir vinaigrette into chicken mixture; cook until heated through, about 2 minutes.